To determine whether enteric flora contribute to glucosinolate metabolism in humans, we evaluated the effect of a standard preoperative bowel preparation on dithiocarbamate excretion after ingestion of glucosinolates from mature broccoli. To prepare glucosinolates, florets from ice-packed broccoli were cut and immediately boiled in a steam- jacketed kettle (8 L water, 5 min). Florets were removed, the remaining liquid was reduced to about half its original volume (over 5 min) and was added back to the cooked florets, and the mixture was homogenized in a Waring Blendor. Samples were taken for analysis and the homogenate was stored at -80 C. Individual doses consisted if 112 g fresh weight broccoli in 182 mL, containing 100 mol non-indole glucosinolates, 0.5 mol isothiocyanates and no residual myrosinase activity; glucoraphanin constituted 76.1% of the glucosinolates.